During 2009 and 2010, the third generation partnership project (3GPP) evaluated open loop beam forming and open loop antenna switching for uplink transmissions in WCDMA/HSPA (Wideband Code Division Multiple Access/High-Speed Packet Access). Both of these techniques are based on that a UE (User Equipment) with multiple transmit antennas exploits the existing feedback, e.g. F-DPCH (Fractional Dedicated Physical Channel) or E-HICH (E-DCH (Enhanced Dedicated Channel) HARQ (Hybrid Automatic Repeat reQuest) Acknowledgement Indicator Channel) to determine a suitable pre-coding vector in an autonomous fashion with the purpose of maximizing the signal quality, e.g. the signal to noise plus interference ratio (SIR), at the receiving Node-B(s). Since the network is unaware of the pre-coding weights that are applied by the UE, the Node-Bs will experience a discontinuity in the measured power level when a change in pre-coding weights occurs.
Recently, there have been proposals for introducing closed loop transmit diversity for WCDMA/HSPA and in [3] a work item was agreed. Contrary to the open loop techniques where the UE decides pre-coding weights, closed loop techniques are based on that the network, e.g. the serving Node-B selects the suitable pre-coding vector with which the signal is multiplied. In order to signal the necessary feedback information from the network to the UE, the Node-B can either rely on one of the existing physical channels (e.g. F-DPCH) or a new feedback channel could be introduced.
Uplink multiple-input-multiple-output (MIMO) transmission is another multi-antenna transmission technique that has been proposed as a Rel-11 candidate for WCDMA/HSPA and in [4] a study item description was agreed. In uplink MIMO transmissions, different data is transmitted from different virtual antennas. It should be noted that closed loop beam forming can be viewed as a special case of uplink MIMO where no data is scheduled on one of the virtual antennas.